This invention relates to integral rocket-ramjet engines.
It is well known that a ramjet engine must attain a certain speed in the atmosphere before it will begin to operate. Because of this requirement a booster rocket motor is employed to bring the ramjet engine to the operable ramjet speed at which time the rocket motor ceases to operate and the ramjet engine commences to operate.
Various arrangements have been used in combination rocket ramjet engines. In the prior art, the boost propellant has been structurally and functionally integrated with the ramjet combustor is as in the patent to Whitmore, U.S. Pat. No. 2,912,820. Whitmore discloses a combined rocket-ramjet engine comprising an engine casing with an air inlet at one end and an exhaust outlet at the other end. A partition separates the casing into upstream and downstream chambers. The downstream chamber contains means for burning rocket fuel. In operation the burning rocket fuel heats, melts, burns, vaporizes or otherwise reduces the partition so that an air flow path is established between the air inlet and the exhaust outlet, thereby permitting operation of the ramjet. The partition is described as being made entirely of metal which is volatilized at or slightly below the temperature at which the rocket fuel burns, or it may be made partly of such material and partly of metal capable of withstanding greater heat.
For certain applications for combination rocket-ramjet engines, compact construction is desirable. One such compact construction uses an inlet diffuser duct which extends along the side of a missile to supply air to a sudden expansion or dump type combustor positioned aft of the missile. In these combustors, the rocket boost propellant is located in the combustor. After rocket motor burnout, the apparatus converts to ramjet operation. The air entrance port to the combustor must be covered until the rocket motor burn is substantially complete; otherwise the forward progress of the missile could be retarded by rocket exhaust gases backflowing through the air intake duct. At the same time transition from the rocket mode of propulsion to the ramjet mode must be relatively fast so that the drag of the missile body does not appreciably reduce the forward speed of the missile.
Mere volatilization of a metal port cover, as disclosed by Whitmore would be too slow. Such volatilization would have to commence prior to completion of the rocket burn, thereby allowing backflow of the rocket gases.
In the prior art the port covers have been ejected. This, however, can present a hazard to the launch and/or chase aircraft. What is desired is a port cover for an integral rocket-ramjet engine which eliminates particle ejecta of significant size.
It is therefore and object of the present invention to provide an improved integral rocket-ramjet engine.
Other objects, aspects and advantages of the present invention will become apparent in following the description of the illustrations.
In accordance with the present invention there is provided an integral rocket-ramjet engine which comprises a port cover for preventing backflow of booster gases into the air entrance during the period of rocket burn, wherein the port cover is made of a material which is rapidly consumed in the brief interim period between the end of rocket burn and the initiation of ramjet burn.